The reticular structures composed by fibrillated films are utilized for reinforcing composite materials having matrices consisting of hydraulic binders (such as e.g. concrete or calcium sulphate) or polymeric matrices (such as e.g. the elastomeric polymers or the unsaturated polymeric resins) and they can be used also as products for the reinforcement of road surfaces or as geotextile products for the reinforcement of grounds.
Such reticulated structures, obtained by means of fibrillation of polymeric films, are well known in the art. These structures are obtained by stretching, according to the extrusion direction, the polymeric films and by successively slitting the monostretched films by means of suitable cutting devices or other slitting means such as sandblasting, brushing, rubbing, etc., in order to cause the formation of a series of longitudinal, parallel, spaced slits, which, due to the subsequent expansion of the film, give rise to the net.
The retiform product thus obtained exhibits, however, the serious drawback of a quite different mechanical strength in the various directions. Actually, such structures exhibit a high mechanical strength in the stretch direction and a low and in any case unsatisfactory mechanical strength in the direction transversal to the stretch direction.
To avoid this drawback it was also suggested to superpose different retiform structures arranged at different angles to one another, or to superpose different retiform structures which have been stretched, fibrillated and splitted at different angles.
Furthermore it was proposed to zigzag-fold a retiform structure on one or more retiform containment structures. Even by increasing the number of zigzag-arranged layers, the resulting composite structure exhibits an unsatisfactory mechanical strength in the various directions due to the considerable discontinuity of the structure resulting from the layer-like arrangement of the retiform structure on the moving basic structure.
Moreover, the zigzag arrangement cannot give rise to structures having a high transversal strength with respect to the longitudinal strength, wherefore it is very limitative with regard to the appliances.